The use of calorimetric and turbidimetric assays for determination of concentration or amount of an analyte in a fluid is well known. Briefly, the analyte is itself able to absorb light or its presence in the sample results in the formation of the compound that absorbs light. Alternatively, the compound itself or its presence in a fluid may result in the formation of turbidity which scatters light, resulting in a diminution in detectable light in a single dimension. Fluorescence assays are also well known; again, the analyte itself may be fluorescent or more commonly its presence in solution results in the formation of a fluorescent moiety; subjecting the fluorescent moiety to a wavelength that it is capable of absorbing results in emission of a somewhat lower wavelength. Typically, in such assays, the detector for the emitted light is orthogonal to the radiation source that effects the emission. The present invention improves the sensitivity of colorimetric and turbidimetric assays by measuring the effect of the generated color or turbidity on the fluorescence of a fluorescent moiety added to the reaction mixture in a configuration typical of fluorescence-based assay.